1. Field of the Invention
The present invention relates to stylets and particularly relates to stylets used to implant pervenous leads.
2. Description of the Prior Art
A pacing lead stylet is normally used in the implantation of a pervenous pacing lead. The pervenous pacing lead is generally constructed of one or more coils of a wire conductor in an insulating sheath surrounding and defining a lumen. The distal end or that portion of the pervenous lead to be placed in the cavity of the heart has an electrode or electrodes affixed to the lead and electrically connected to the helically coiled wire conductors. The proximal end of the pervenous lead has a terminal assembly. The terminal assembly includes terminals electrically connected to the helically coiled wire conductor. This terminal assembly is adapted to be placed in a socket in the neck of an implanted cardiac pacer.
The helically coiled construction of the pervenous lead renders the lead most difficult to pass through an appropriate vein to the appropriate cavity of the heart. A stylet, when inserted into the lumen, imparts some rigidity to the lead enabling the physician to exert some force on the lead. However, a stylet with an unprotected distal tip can penetrate between the helical coils. Penetration is most likely in those patients having a tortuous vein, and is potentially injurious to both the performance of the lead, and the patient.
Further, there are pervenous leads which have a preformed curve. One such lead is the atrial "J" lead, in which there is a rather pronounced curve. Since precurved leads must be straightened for placement, with available stylets difficulties are encountered such as penetration between coils or the catching of the stylet tip on a coil.
There have been a number of proposals for stylet constructions which reduce the risk of penetration while providing sufficient rigidity for pervenous leads and related devices.
U.S. Pat. No. 4,548,206 to Osborne discloses a CATHETER WIRE GUIDE WITH MOVABLE MANDRIL. The movable mandril is tapered towards its distal end which is an elongate bulb.
U.S. Pat. No. 4,554,929 to Samson et al. discloses a CATHETER GUIDE WIRE WITH SHORT SPRING TIP AND A METHOD OF USING THE SAME. The spring tip surrounds a reduced section extension of a guidewire shaft.
U.S. Pat. No. 4,498,482 to Williams discloses a TRANSVENOUS PACING LEAD HAVING IMPROVED STYLET. The stylet has a constant diameter at its proximal end, a ball at its distal end and a tapered section in the transition of the stylet from a constant diameter to the ball portion. This pacing lead stylet has a ball placed on the distal end of the stylet to prevent penetration between the coils. However, the ball on such a stylet can get caught by one of the coils preventing its advancement or withdrawal within the lumen of the pervenous lead.
The non-analogus U.S. Pat. No. 4,456,017 to Miles discloses a COILED SPRING GUIDE WITH DEFLECTABLE TIP. Its core wire has a reduced section at its distal end which is permanently, and eccentrically, affixed to a head member. Proximal movement of the core wire causes the guide to assume an arcuate shape.
U.S. Pat. No. 4,454,888 to Gold discloses a CARDIAC PACING LEAD WITH CURVE RETAINER. A flat spring near its distal end causes the lead to assume a J-shape when a stylet is withdrawn from that portion of the lead.
U.S. Pat. No. 4,271,847 to Stokes discloses a TEMPORARY ADJUSTABLE BIPOLAR LEAD including a coaxial sliding pacing lead for establishing a connection between a chamber of a heart and a pulse generator.
The non-analogus U.S. Pat. No. 3,906,938 to Fleischhacker discloses a COIL SPRING WIRE GUIDE including a coil spring surrounding a core wire which is welded to a spring tip. The core wire is substantially cylindrical except in its distal portion where it is flattened adjacent its joinder to the spring tip.
The non-analogus U.S. Pat. No. 2,024,982 to Scott discloses a SURGICAL INSTRUMENT including a stylet having a flat, tapered stylet portion near an ellipoidal shaped tip.
United Kingdom Patent Application No. 2 064 963 A describes a STYLET having a tapered portion terminating at a ball in its distal end and corresponds to U.S. Pat. No. 4,498,482 referred to above.
Swedish Patent No. 193885 discloses A CATHETER INTENDED FOR INTRAVASCULAR CATHETERIZATION having an arcuately curved distal end which is straightenable by an inserted stylet. The stylet has a rounded cylindrical distal end portion.
The non-analogus prior art patents are not considered to be citable prior patents with respect to the claimed stylet and are only being cited herein to comply with the duty of disclosure.
Moreover, none of the foregoing patent publications disclose a pacing lead stylet which completely addresses concerns about penetration while having a selective balance between rigidity and flexibility to be usable with both straight and precurved pacing leads.